mutant neighbours differentiated by a single point mutation [1]}, [2]}, [3]}, [4]}.
These \(D\)  neighbouring genotypes are available for natural selection.
Then, at the SSWM limit, only one of these neighbouring sequences can be fixed, chosen among those with fitness values higher than the wild-type fitness.
Once a new mutant is fixed, a new set of \(D\)  mutant neighbours is available for selection.
Repeating this process unfolds an evolutionary path until it reaches a local (or global) fitness peak in the rugged landscape.
However, if a local peak is reached (i.e. the state when all \(D\)  accessible genotypes have strictly lower fitness values), then the evolutionary process is “trapped” because any other fitter genotype is at two or more point-mutational steps away (i.e. only attainable by “descending” through a valley in the fitness landscape).
